Source Directivity is a Key Mechanism of Imaging Illumination Loss under Rugged Seabed

Abstract In offshore explorations, the amplitudes and frequencies of seismic data under the rugged seabed are often distorted, and the imaging amplitudes are partially attenuated with obvious energy banding distributions. The attenuation critically affects the quality of seismic profiles, reducing the effectiveness of seismic data interpretation and undermining the reliability of assessments for oil and gas resource development. Furthermore, the mechanism behind the attenuation beneath rugged seabeds remains unclear, as extensive researches have yet to explain this phenomenon, presenting a significant challenge in the field. In practice, the observed amplitude reductions may result from a combination of intrinsic attenuation and illumination effects. In order to investigate the influence of rugged seabed on seismic wave propagation and imaging, we construct 2-D and 3-D rugged seabed models, conducting acoustic and elastic simulations, illumination analysis and pre-stack depth migration imaging. In this study, we identify a specific illumination-related mechanism: the coupling between source directivity and rugged seabed topography, which leads to the banded amplitude variations beneath the bulges and depressions of the seafloor, which can be observed in real seismic profiles. Exploring the interaction between the source directivity and rugged seabed can serve as a guidance for effective amplitude compensation of seismic profiles for offshore explorations, and provide high-quality seismic data for interpretations.